Response of Winter Wheat Canopy Spectra to Chlorophyll Changes Under Water Stress Based on Unmanned Aerial Vehicle Remote Sensing

In order to explore the characteristics of canopy reflectance of winter wheat responding to leaf chlorophyll changes in each growth period under water stress, a total of three water gradient treatments were set for 11 wheat varieties (divided into strong, general and weak drought resistant strains) in the growth season from 2020 to 2021, including two irrigation treatments (jointing and flowering), one irrigation treatment (winter, turning green, jointing, 7 days after jointing and 14 days after jointing) and no irrigation, The correlation between chlorophyll and reflectance was analyzed. The narrow band spectral indexes most sensitive to chlorophyll were selected by using the random combination of wavelengths (simple ratio (SRSI), simple difference (SDSI) and normalization (NDSI)) and linear fitting methods. The results showed that: (2) With the development process and the drought resistance of varieties weakened, the difference of canopy reflectance in near-infrared region between different treatments gradually increased. (3) The high value of the linear fitting determination coefficient of chlorophyll and narrow band spectral index is concentrated in the green (445 similar to 591 nm) and red edge (701 similar to 755 nm) bands. The SRSI index of drought resistant and drought-resistant strains had the highest precision of chlorophyll retrieval at the flowering stage, reaching 0.762 and 0.811 respectively; The NDSI index of general drought-resistant strains had the highest precision at the filling stage, which was 0.732. This study has a certain reference value for revealing the reflectance response of chlorophyll change under water stress in different key growth stages of winter wheat and differences among varieties. It can lay a foundation for efficient screening of drought-resistant wheat varieties based on unmanned aerial hyperspectral technology.